Metal-stretching press



March 2, 1948. P A. M. GREENE, JR, Er AL 2,

METAL STRETCHING PRESS Filed Sept. "22, 1944 3 Sheets-Sheet I CIZIZZ' IINVENTORS ARTHUR H. GREENE- JR. WALTER ER NST ATTORNEYS March 2, 1.948-A. M. GREENE, JR, ET AL ,4

- mam. s'rjnmcame mass 7 Filed Sept. 22, 1944 s Sheets-Sheet? llINVENTORS- ARTHUR M. GREENE JR.

WALTER ERNST BY ATTORN EYS March 2, 1948.

JTE

A. M. GREENE, JR, ET AL METAL STRETCHING PRESS Filed Sept. 22,- 1944 aSheets-Sheet 3 INVENTORS ARTHUR M. GREENE JR. WA LTER ERNST ATTORNEYSPatented Mar. 2, 1948 UNITED'STATES PATENT OFFICE BIETAL-STRETCHINGPRESS Arthur M. Greene, Jr., Princeton, N. J., and Walter Ernst, MountGilead, Ohio, assignors to H-P-M Development Corporation, Wilmington,Del., a corporation of Delaware Application September 22, 1944, SerialNo. 555,238

11 Claims. 1

This invention relates to method and apparatus for stretching sheets ofmaterial into predetermined configurations.

In the art of metal stretching it is customary to grip a sheet of metalalong the edge thereof and to advance a single die or forming memberinto the said sheet so as to stretch the material into the desiredconfiguration. Ordinarily, the gripping jaws are manually manipulated tobe moved closer to the stretching member as the operation progresses sothat the sheet does not rupture or so that the sheet may be morecompletely formed around the punch or die member.

It will be apparent that the manual manipulation of the gripping membersrequires a highly skilled operator and, at best, can only approach themost desirable conditions for a stretching operation.

It is a primary object of the present invention to provide a stretchingpress which will produce superior workpieces.

It is another object to provide a stretching press in which the tensionin the sheet being stretched is automatically controlled.

It i another object of the present invention to provide automatic meansfor moving the gripping members during the stretching operation,

It is another object to provide a stretching press in which anypredetermined tension may be maintained on the sheet, or in any portionthereof during the stretching operation.

It is another object to provide a method and apparatus for stretchingsheets into more or less complex configurations. I

These and other objects and advantages will become more apparent uponreference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view of a metal stretching press constructedaccording to this invention;

Figure 2 is an enlargement of a portion of Figure 1 showing in greaterdetail the swivelled laws and the valve arrangementassociated with thejaw reciprocating motor;

Figures 3, 4 and 5 are diagrammatic views showing diiferent stages of astretching cycle;

Figure 6 is a modification showing a plurality of gripping membersattached to a crosshead and a single jaw reciprocating motor;

Figure 7 is a view showing a plurality of jaws and jaw reciprocatingmotors in association with a pressing member of irregular shape; and

Figure 8 is a View of a modified arrangement for the jaw and slidereciprocating motor showpower means for moving thesame; v

2 General arrangement In general, a stretching press constructedaccording to this invention comprises a frame having suitably mountedtherein, in any desirable manner, a die carrying reciprocable platen.Motor means, preferably fluid operable, are provided for reciprocatingthe platen thereby to advance the die or punch into the work. Theworkpiece is adapted to be gripped by a pair of g ipp members mounted onthe press frame on either side of the said platen. According to thisinvention, the jaws are swivelled to crossheads which latter areautomatically reciprocated during the stretching operation. The movementof the crossheads or jaw carrying slides is automatically controlled sothat a predetermined and substantially constant tension is maintained inthe sheet throughout the stretching operation. The jaws and slides towhich they are attached are preferably reciprocated by a fluid motorwhich has associated therewith suitabl valving means for initiallypositioning the said jaws and for thereafter eiiecting theaforementioned automatic control.

The valve which automatically controls the motor connected with theslide comprises a pilot operated valve which is hydraulically connectedwith a plunger associated with the gripping jaws, In response to apredetermined tension on the sheet, a predetermined pressure isdeveloped by the said plunger and i transmitted to the pilot operatedvalve. The pilot operated valve is adapted to respond to a predeterminedpressure to permit the exhaust of fluid from one side of the slide motorthereby permitting the latter to move. I

According to one modification the pilot operated valve is-connected witha source of fluid pressure so that the slide is positively moved byfluid pressure rather than by the tension in the sheet.

According to another modification a plurality of gripping means areprovided on either side of the platen and the tension in the sheet maybe varied from place to place as required by the shape of the pressingmember.

According to still another modification a plurality of jaws is providedon either side of the the other.

Detailed description Referring to Figure 1, the press according to thisinvention comprises a frame I!) having mounted therein, or integraltherewith, a main cylinder H within which is reciprocable the ram l2which carries a platen 13. A die or punch IA is attached to the platenl3 in any suitable manner.

Arranged on either side of the platen I3 are the gripping or jawstructures [5 and I6. Each of the jaw structures comprises a slide orcross-- head ll which is slidably mounted on the presspiston-cylinder-arrangement at 20 so that movement to the left by thejaw I9 is effective to create a pressure which, when conducted to thecylinder 42, actuates the plunger 4| and the valve member 38.

Connected with the discharge side of the pump 29 by means of the conduit45 is a distributing valve 46 which also has connected therewith theexhaust conduit 41, the conduit 48 which leads to the upper end of thecylinder l l and, the con- I duit 49 which leads to the lower end of thecylinframe 10 such as by the way and gib arrange-e ment indicated at I3.Swivelly attached .tothe slide member ll are jaw units comprising agripping member l3 and a, piston and cylinder arrangement it. Thepiston-cylinder arrangement. 1

is connected by the trunnion 2| to the slide mem.- ber ll. Since the jawstructures at each side of the platen are identical, a description ofthe one at the right of the platen, as seen in Figure 1, will sufiicefor both.

Affixed to the side of the slide member I"! opposite the platen I5 is aplunger 22 which extends into a cylinder 23 mounted on the bed ill. Theplunger 22 extends completely through the said cylinder and has a piston24 thereon within the cylinder so as to form a fluid operable motorhaving advancing and retracting areas which are equal.

Connected with the right end of the cylinder 23 is a conduit 25 whichleads to a four-way valve 26. Connected to the left end of the cylinder23 is a conduit 2i also leading to the valve 26. The valve 26 issupplied with pressure fluid by a conduit 23 from the pump 29 which isconnected by a conduit 36 with a reservoir 3|. The valve 2% also hasconnected thereto an exhaust conduit 32 which leads directly to thereservoir 3 I. The

valve 26 is movable into a first end position tointerconnect theconduits 28 and 35 while simultaneously connecting the conduits 21 and32 and, into a second end position to interconnect the conduits 2'? and23 and the conduits 25 and 32.

The valve 26 is also movable into an intermediate position wherein thefluid communication between the said conduits in interrupted.

Also connected with the left end of the cylinder 23 is a conduit 33which leads to a valve. 34, the valve also being connected by theconduit 35 with the right end of the cylinder 23. The conduit 35comprises the check valve 36 which permits the fluid flow from the valveto the cylinder but not vice-versa.

The valve 34, more clearly shown in Figure Z, comprises a valve casing31 within which is reciprocable a valve member 33. The valve member 36is urged into its right hand end position by a spring 3.9, the thrust ofwhich may be varied by adjusting the hand wheel and screw arrangement atit. In its right hand position, the valve member 38 interrupts fluidcommunication between the conduits 33 and 35. Opposite the spring 39 isa plunger M which is reciprocable in the cylinder Q2. The plunger 4! isoperable, when pressure fluid is supplied to the cylinder 42 from theconduit 43, to move the valve member 38 leitwardly so as to interconnectthe conduits 33 and 35.

The conduit 63 is connected with the pistoncylinder arrangement at 29associated with the jaw I3. Preferably the conduit 43 comprises aflexible portion M which permits the free movement of the slide llrelative to-the valve am The conduit 43 is connected into the left endof the der H. The valve it is movable into position to interconnect theconduits 48 and 5 and the conduits 49 and t! or into position to connectthe conduits 48 and 4'! and the conduits l9 and 45.

Referring nowto Figure 6, a modification is shown wherein the pressingmember 50 is of an irregular shape; being larger at the one end than atthe other. The press shown in Figure 6 comprises a plurality of jawmembers 5| which are connected with a plurality of piston-cylinderarrangements at 52 the latter being universally connected with acrosshead or slide 53 by the pivotal connections 52a and 52b. ihe slide53 is pivoted as at 54 to a plunger 55 of the motor 55. As in the caseof the motor 23, the motor 55 has equal advancing and retracting areas.

A valve 5'! similar to the valve 34 is connected with the opposite endsof the motor 58 and is piloted by fluid conducted thereto to the conduit58. The conduit 58- is connected with the several piston-cylinders 52 sothat the average pressure in the said piston-cylinderarrangement isconducted to the valve 57. It will be apparent that the arrangement inFigure 6 is such that a predetermined tension may be maintained across asheet which is being drawn by an irregularly shaped pressing member.

Referring to Figure '7, there is shown a modified arrangement of thisinvention wherein the pressing member til is of relativelycomplexvconfiguration. A plurality'of jaws 6i grip the workpiece alongthe margin thereof, each of the jaws ill having associated therewith apiston-cylinder arrangement $2M Each of the piston-cylinder arrangements62'isipivotallyconnectedwith an individual'slide '63 at 63c, and each ofthe latter has associated therewith the motor 6 3.

Eachof the motors 64xhas connected thereto a valvetfi similar .to thevalves 3t and 51 and each valve' is actuated by fluid 'pressureconducted thereto from the associated piston-cylinder 62 by a conduit66;.

It will be apparentthat'any desired tension may .be'maintained inanyportionofthe sheet merely by adjusting the individual valves 65.Accordingly, it is possible to form a workpiece of relatively complexconfiguration without overstressingorrupturing or underforming any ofthe various portions thereof. It will be noted that the jaws at arepivoted attwo points so that they may:follow the outline of thework-piece as it is being formed.

Referring now toFigure 8, there is shown a modified arrangement whereinthe jaw and slide reciprocating motor is positively moved during thestretching operation. In this figure the jaw and slide reciprocatingmotor it. has therein the double acting piston H to which is attachedthe plunger .12 which is, in turn, connected with the slidemember of thejaw structure.

Connected with the right end of the cylinder lii is'a conduit 73 whichconnects with the valve l4 arid,- connectedwiththe left end of thecylinder it is a conduit lfial's'o leadingtothe valve i l.

The valve 14 is supplied with pressure fluid by a conduit 16 whichconnects with the discharge side of the pump 11. The pump 1! and thevalve 14 are also connected with a reservoir 18 by the conduits l9 and80, respectively.

p The valve 14 is movable into position to directpressure fluid eitherto the right or to the left end of the cylinder in while simultaneouslyexhausting the other end or, into an intermediate position forinterrupting said fluid connections.

Connected with the conduits 13 and 75 are a pair'of conduits 8| and 82which lead to a valve 83. The valve 83 also has connected therewith theconduit 84 which is connected with the discharge side of the pump 1'!and a conduit 85 which is connected with the reservoir I8. The

valve 83 comprises a valve member 86 which is normally positioned tointerrupt fluid communication between the various valve conduits. Anadjustable spring 81 at the right endof the valve urges the valve member86 leftwardly until the collar 88 engages the end of the valve casing.

A spring 89 at the left end of the valve urges the valve member 86rightwardly until the collar 90 engages the end of the valve casing. Aconduit 9| is connected into the spring casing 92 and is also connectedwith the piston-cylinder arrangement associated with the jaw and slidestructure attached to the plunger 12.

Itwill be apparent that a predetermined pressure within the springchamber 92 conducted thereto by the conduit 9| is effective to move thevalve member 86 rightwardly thus establishing fluid communicationbetween the pump 11 and the right end of the cylinder whilesimultaneously connecting the left end of the cylinder 10 with exhaust.The plunger 12 is thus positively moved toward the platen of the press.

Operation position so that the fluid in the opposite ends of the motors23 is trapped.

The operator then shifts the valve 46 to move the plunger I 2 and thepunch or die member [4 upwardly. The condition prior to the stretchingoperation is shown in Figures 1 and 3.

After the die has moved upwardly a short distance, the conditionsexisting are illustrated in Figure 4. In this figure .the movement ofthe die member has created a predetermined tension in the portion of thesheet between the die and the jaw members on either side thereof. Thetension in the sheet creates apredeterm-inedprese sure in thepiston-cylinder arrangement which, when conducted through the conduit 43to the cylinder 42 actuates the plunger 4| to move the valve member 38leftwardly against the thrust of the spring 39 thus interconnecting theconduits. 33 and 35. After the valve member 38 has been shifted tointerconnect the opposite ends of the ,motor 23, the tension on thesheet is efiective to move the slide l1 and plunger 22 leftwardly untilthe valve 34 again closes.

In this manner the piston-cylinder arrangement 20 acts as a signalcylinder for the main arrangement 20 which moves in response to thetension created in the work piece, but it is the signal cylinder 20carried by it, which moves in response to said tension. It is to befurther noted that the pivot points of the pivotal connections at 2| ofthe gripping arrangements 20 are moved automatically in response to a.predetermined tension in the sheet in a direction at right angles to theupward movement of the pressing member,

As the stretching cycle continues the parts move from their Figure 4position into the position indicated in Figure 5 where the workpiece issubstantially completed. It will be apparent that throughout thestretching operation a substantially constant and predetermined tensionhas been maintained in the portions of the sheet between the pressingand the edges thereof which are gripped by the jaws.

It should be noted that as the work piece is formed, as shown in Figures3, 4, and 5, the gripped edges of the sheet material have moved towardsthe forming member substantially at right angles to it, subject only toa slight angular deflection caused by the tilting of the member 28 aboutthe pivot 2|. Thus, said gripped edges are automatically paid outtowards said forming member in a substantially right angular relation toit, said paying out of said edges being in response to a predeterminedtension in said sheet material.

Should it be desired to move the jaws even closer to the platen thantheir Figure 5 position, the operator may shift the valves 26 whilepermitting the die M to continue its advancing movement.

The operation of the embodiment shown in Figure 6 is similar to theoperation of the embodiment of Figure 1 except that the slide 53 is freeto assume an angular position relative to the press frame thuspermitting a workpiece to be stretched which is substantially wider atone end than the other. It will be apparent that the modification ofFigure 6 also provides for a substantially constant and predeterminedtension to be maintained in the sheet at all times.

The modification illustrated in Figure 7 operates in a mannersubstantially identical with the modification of Figure 1 except thateach gripping member or jaw is separately moved so that a workpiece ofcomplex configuration may be formed. It will be noted that the pressurewhich 'is maintained on the portion of the sheet associated with eachjaw is individually adjustable so that one portion of the sheet may bestretched a great deal more than another portion without in any waydetracting from the quality of the finished workpiece.

The modification shown in Figure 8 provides power means for moving thejaws and thereby eliminates the possibility that the inward movement ofthe jaws may be halted before the forming operation is completed. Infact, with the arrangement shown in Figure 8, the margins of theworkpiece may be formed even beyond the limits of the die member thusproviding means for eliminating spring-back should it be desiredparallel side portions thereon.

It will be apparent that various modifications may be made in thestructure of this invention without in any way departing from the spiritthereof. For example, the motors 23 could be contained within the bed 20if so desired thereby rangement. Also, the jaws l9 could be replaced Itwill be obvious that the piston-cylinder-arrangements at 20 providemeans for directly measuring the tension in: the .sheet.-l;llflthusinsuring that the valve 35 311111 be actuated at-the propertime. V'Also, it will be obvious-that;the valve 34 will, in mostinstances, operate to throttle the flow of fluid from the left end -of--the motor 23 rather than intermittently exhaustingthe same.

It i will also be apparent, upon reference to Figures 6 and 7,- thattlie worksheets-could' be slit between-the jaw membersin order to;facilisired.

It will be understood; thatwe desire-topomprehendwithin ourinventionsuch modifications as may come withinthe scope ofthe inventionand the claims.

Having thus fully described our invention,what we claim as new anddesireto secure by Letters Patent, is: l

1. A method of forming workpieces from ductile sheet material with asingle forming member "which comprises, rigidly gripping the said sheetat, a plurality of l points on either side. of said forming member and,advancing said forming member into said sheet While automatically.positively, paying out saiclrigidly gripped points sub-'stantiallyatright angles-to said forming member in response to asubstantially constant-and predetermined unit stress in said materia1between each of said gripped pointsand said forming member.

.2. A method of forming: workpieces from ductile sheet material whichcomprises,-;rigi dly.gripping apair of opposite edges of said sheetby abetweeneach of said grippingmembers and said forming member.

3. A press for shapingmetal sheets comprising a frame, a reclprocablepressinga ember carried there a p r 10f gri in "mea slidablv mounted onsaid irame cn 'oppos1tesldes;- of said pressing member, eachot said.-gripping'mean ,in-

cluding jaw members.,;swivelled thereto, ,fluid'voperable .motor meansfor reciprocatingsaid-pressing member relative to saidgripping means,fluid operable motor means for initially 1i positioning said grippingmeans relative-to said pressing member, and fluidpressure vcontrol meansfor l said gripping means automatically operable in response tov apredetermined tensi-onin said sheet to cause said second mentionedmotorqmeansto -move said grippingmeans toward-each-ptherin a planevwhich is substantially at right angles to said pressing member.

4. A press fOY'ShalJingIllBtdl sheets; comprising a frame,a press platenreciprocable-relative to said frame and adapted to mount adiemember,

c slide means arranged on. saidframe on either side-oi said pressplatenand movable relative thereto, eachofsaid slidetmeans includinga :jaw

member having associated therewith a;-pist oncylinder arranementppivotallysecured to;.;said

slide-means; first motor; means for; reciprocating e-said, presssplaten;relativatq a: she tgri pe by and said slide means,-- valveIneansconnected with -;--.said :fluidsourcaand vsaid second motor means'iandlmovable intoia position to interrupt fluid =communioation betweensaid-motormeans and tsaidqfluid:source'for maintaining said slide meansimanyi predetermined position,. and fluid control means associatedwithsaid second motor means l-responsiveto a, predetermined pressure in said.piston-cylinder arr,ange,ment to .by-pass fluid aroundsaid valve meansto-cause said slide means to move relative to said platen. tate theshaping of complex workpieces if ,s0 de-' 5.. 1A presslforshapingmetaLisheets comprising-ca frame,aplaten adapted to mounta diezmember reciprocable relativeto said frame, slide imeansqslidable, 1011@said. frame on. either. side of ssaid -platen jawmeansztassociated witheach of saidislide means. and including 7 a piston-cylinder arrangementpivotally connected with said slide means, reciprocable fluid operablemotor. means coi1nected :vvith said slide means for. reciprocatingv-the-sam e,- .-valve means operable to connect said .-motor-i.meanswith a source ofifluid pressure or to disconnect said gmotor means ifrom said fluid sourceand'f-rom exhaust, othervvalve meansoperable tosimultaneously.connectsaid motor means awithesaidsource of fluidpressure and with exahaustsandfluidpressure actuated means responsivertoapredetermined pressure in said pistoniacylinder arrangement foroperating said other valve ameans.

.- 6..:A pressfor shaping ductile sheet material into-workpiecescomprising a frame, a vertically reciprocable press platen carriedbysaid frame, a pair of transversely-slidable crossheads slidably carriedon said frame on either side of said 140 platen, each of saidcrossheadshaving pivoted thereto cylinder means, each of said cylinder meanshaving a, piston therein and each of said 1 pistons having connectedtherewith a jaw member adapted togrip a marginal portion of said 5sheet, fluid operable motor means mounted on said; frame having plungersreciprocable therein and connected with said crossheads, said plungershavingequal, opposed areas thereon, agfluid source for supplyingactuating fluid to said areas,

; .valve means movable to connect one or the other of said areas withsaid source, said valve also being movable to interrupt fluidcommunication 1 between said areas and said source, other valve vmeansinterconnecting said areas and normally positioned topreventfluid'flowtherebetween, and

[fluid pressure responsive control means for said other valve operablein response toa predetermined fl-uid ,.pressure in said I cylinder meansto causeisaid other valve to move into position to hydraulicallyinterconnect said. areas, andmeans for, adjusting the pressure at whichsaid control .-means is responsive to maintain any .desired.-predetermined. constant tension in fsaidv sheet duringreci rocation ofsaid platen.

7.. A press for shaping. ductilev sheet materialintosworlzpieces.comprisinga frame, a die carrying platen reciprocablerelative to said frame, a cro'sshead slidablymounted .on ,said frame oneither side of saidplaten, said crossheads and said frame havingcooperating guidingmeans to cause saidgcrossheads toamove transversely.of said frameand also .to, swing in said frame, .each of 1 ?'-.l -i f051 hav n p v iel e r thereto .pl raliir ,aden ne-m b s l a h twli has x-va s d te t erewi h-a lrif scvllnqen area ment, fluid operable motormeans pivotally secured to said crossheads for initially positioning tlatter relative to said press platen, means for ac rating said motormeans for accomplishing initial positioning and for thereafter trappingthe fluid in said motor means, valve means connected with said motormeans for bypassing the same to allow yielding movement of saidcrosshead, and fluid pressure responsive hydraulic control meansinterconnected with said valve means and with said piston-cylinderarrangement operable by pressure variations in said piston cylinderarrangement to cause said valve means to regulate the yielding movementof said crosshead in response to a predetermined average tension in saidsheet.

8. The combination in a metal stretching press having a frame and apressing member reciprocable relative thereto, of means slidably mountedon said frame on either side of said pressing member for grippingopposite marginal portions of said sheet, each of said gripping meanscomprising a jaw member universally pivoted to a plunger, a cylinderwithin which said plunger is reciprocable, a slide to which saidcylinder is pivotally connected, and motor means connected with saidslide for reciprocating the same so as to initially position said jawmembers; and fluid control means operable by pressure created in saidcylinder by the pull of said jaw member on said plunger to cause saidmotor means to move said jaw member toward said pressing member as thelatter advances into said sheet.

9. A press for shaping ductile sheet material comprising a frame; apressing member. reciprocable relative to said frame; workpiece grippingmeans slidably mounted on said frame on either side of said pressingmember, said workpiece gripping means comprising a jaw member, apiston-cylinder arrangement, a slide member and a fluid operable motor,said jaw member being pivotally connected to said piston-cylinderarrangement and said piston-cylinder arrangement beil'lg pivotallyconnected to said slide member; means connecting said slide member withsaid fluid operable motor; valve means operable to entrap fluid in saidfluid operable motor; and fluid pressure control means for said valvemeans interconnected between said fluid operable motor and saidpiston-cylinder arrangement, said fluid pressure control means beingresponsive to a predetermined pressure in said piston-cylinderarrangement so as to release said entrapped fluid by controlling saidvalve means.

10. A method of forming workpieces from sheet material which comprises,rigidly gripping a sheet of material along at least two edges thereof,effectingrelative movement between said sheet and a forming member so asto form the Workpiece, and automatically maintaining a positivelycontrolled tension in said sheet at a substantial- 1y predeterminedconstant amount throughout the whole of said relative movement and theen tire formation of said workpiece by automatically positively payingout said rigidly gripped edges of said sheet at substantially rightangles to the plane of said forming member in response to said tension.

11. The combination in a metal stretching press having a frame and a diecarrying platen reciprocable relative to said frame, of workpiecegripping means slidabiy mounted on said frame on either side of saidplaten, said workpiece gripping means comprising slide means, jawmembers pivotally connected with said slide means, and motor meansselectively operable for reciprocating said slide means to initiallyposition said jaw members; and control means connected with said motormeans so that said motor means may cause further automatic movement ofsaid slide means and the pivot points of said pivotal connections, saidcontrol means being automatically operable in response to apredetermined tension applied to oppose the pull of said jaw members inthe workpiece to thus cause said motor means to move said slides andsaid pivot points relative to each other in timed relationship with thereciprocation of said platen, said relative movement of said slides andsaid pivot points being at right angles to the reciprocation of saidplaten.

WALTER ERNST. ARTHUR M. GREENE, Js.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,461,471 Bancroft July 10, 19231,622,590 Jolstad Mar. 29, 1927 1,710,261 Kellogg Apr. 23, 19292,006,468 Longren July 2, 1935 2,129,774 Kohner Sept. 13, 1938 2,245,723Salzmann June 17, 1941 2,279,964 Berliner Apr. 14, 1942 2,279,965Berliner et al Apr. 14, 1942 2,289,584 MacMillin et a1. July 14, 19422,301,960 Lermont et al Nov. 17, 1942 2,302,953 Pocock Nov. 24, 19422,326,470 Lermont et al Aug. 10, 1943 2,342,437 Summers Feb. 22, 19442,346,213 Flowers Apr. 11, 1944 2,349,520 Ripley May 23, 1944 2,371,587Seifried Mar. 13, 1945 2,378,413 Lermont et a1 June 19, 1945

